1. Field of the Invention
This invention pertains to the field of optical instrumentation. It relates more specifically to remote observation instruments comprising a complex optical path and requiring precise pointing.
2. Description of the Related Art
In the field of remote observation, numerous devices require maintaining a stable pointing of the observation instrument, independently of the perturbations generated by the numerous sources of vibrations, random in frequency and amplitude, created by the mechanical assembly and the support device.
This is the case, for example, of image acquisition means as they are known in the field of planetary observation, by satellite or by aircraft, typically using a bar or matrix detector and a movement of the sensor platform, making it possible to scan a swath of the planet's surface that is being observed.
The pointing of a stationary point (line of sight) is therefore necessary for the reconstitution of images and, failing this, it is desirable to know the instantaneous movement (commonly called “jitter”) of the line of sight.
It is clear that the higher the resolution of the image, the greater the need for a stable line of sight.
Along the same lines, devices for communication by laser, for example between satellites, also require extremely precise pointing of their line of sight. One problem that is analogous to the line of sight stabilization is then posed.
Solutions for stabilization of optical line of sight have already been considered. One of the known solutions is to place the optical platform on a vibration damping system, for example an active system for detecting vibrations and for correcting these vibrations in real time. However, these devices are complex, restrictive for the design of the instrument, and often exhibit inadequate performances for the remote imagery systems currently envisioned. Furthermore, the optical assembly itself can generate perturbations in the line of sight, which, of course, are not corrected by a system as previously described.
Another solution is then provided by the user, known in the art, of a so-called inertial reference, such as, for example, a star, whose position is essentially stationary relative to the earth over the period of acquisition of an image.
Another solution is disclosed in the U.S. Pat. No. 6,700,109 B2 of 2004. In this document, a device for active correction of line-of-sight vibrations uses a pseudo-inertial reference generator that takes the form of a laser source, stabilized inertially with an actual active monitoring device.
This laser source is arranged in such a way that its beam essentially follows the optical path of the light rays coming from the observed zone such that the sight modifications of this pseudo-inertial source can be considered as being due integrally to the vibrations of the optical platform. These vibrations are then detected by a matrix detector that is placed in the vicinity of the image sensor and corrected by manipulating the orientation of one of the mirrors for reflecting the light beam on the optical path.
However, the implementation of an active monitoring system at the input of the optical instrument is complex and has a strong impact on the design of the instrument, for example imposes the creation of an electrical network for supplying this system and modifies the heat monitoring constraints, which increases the cost of the instrument.